| The researches on impacts of extreme precipitation change on river runoff and sedimentchnage can provide scientific basis for flood warning and important reference forwater resources management. Based on the precipitation data from12meteorological stationsduring1957to2012and river runoff, sediment data during1957to2011in theHekouzhen-Longmen region, the temporal and spatial variation of the average precipitationand extreme precipitation in long-term trends were analyzed and the dynamic changes andtrends of runoff and sediment were studied, using the methods inear trend estimate,Mann-kendall non-parametric tests, cumulative anomalies and spatial kriging. The bestindicator of extreme rainfall change was selected, finally the quantitative assessment of riverrunoff and sediment variation caused by human activities and extreme precipitation changewas conducted. The main results were as follows:(1) Based on the precipitation data during1957to2012, the spatial and temporalvariation of precipitation were analyzed in the Hekouzhen-Longmen region. The averageannual precipitation was451.5mm, the average precipitation in flood season was333.5mm,and these two indicators were gradually increased from northwest to southeast in space. Theannual precipitation mainly concentrated in May to September which took over81%of theannual precipitation, and the precipitation in flood season took over73%of the annualprecipitation. The annual precipitation, the precipitation in flood season and the precipitationin spring, summer and autumn decreased non-significantly while the precipitation in winterincreased non-significantly.(2)7internationally accepted and commonly used extreme precipitation indicators (R10,R50, R10p, R5d, SDLL, R95p, R95t) were selected to study the temporal and spatial variationof extreme precipitation during56years in the Hekouzhen-Longmen region. These7indicators were gradually increased from north to south in space, the maximum values weremostly occurred in Qingshuihe station and the minimum values were mostly occurred inYanan station. These7indicators were gradually decreased during the period, the R5ddecreased significantly by0.24mm/a. (3) Based on the daily precipitation data of the Hekouzhen-Longmen region during1957to2012and the sub-basin Huangfuchuan basin during1954to2004, the spatial andtemporal variation of rainfall erosivity was studied using the modified Richardson estimatemethod. The average rainfall erosivity in the Hekouzhen-Longmen region was1329.6MJ· mm/(hm2·h·a) during56years, and the value was gradually increased from northwest tosoutheast in space with the lowest center in Qingshuihe station. The rainfall erosivity inQingshuihe station and Wuzhai station were increased non-significantly while the rest of thestations were decreased non-significantly. The average rainfall erosivity in Huangfuchuanbasin was1136.1MJ· mm/(hm2·h·a), and the value was gradually increased from northwestto southeast in space with the lowest center in Wulangou station and highest center inChangtan and Shagedu. The rainfall erosivity in Huangfuchuan basin was non-significantlydecreased trend.(4) Based on the river runoff and sediment data in the Hekouzhen-Longmen regionduring1957to2011, the dynamic change and variation trend of river runoff and sedimentwere studied. The average runoff was44.58×108m3with a decreasing trend by0.96×108m3/a.The average sediment was5.60×108t with a decreasing trend by0.19×108t/a. The abrupt yearwas1979which was determined by the method of Mann-Kendall test and cumulativedeparture.(5) Took1979as abrupt year of river runoff and sediment, the relation between riverrunoff, sediment and precipitation indicators were established in3periods: reference period(1957to1979);the test period (1980to2011) and whole period (1957to2011). The resultshowed that the linear correlations between river runoff, sediment and R95p, R,R10p and FPwere better than that of yearly precipitation P. Moreover. the linear correlation between riverrunoff, sediment and precipitation indicators, R95p, R, R10p and FP was selectable and FPwas the best indicator.(6) Took P and FP as precipitation indicator, R95p and R10p as extreme precipitationindicator, river runoff and sediment variation caused by human activities and precipitationchange was estimated respectively during1957to1979, the estimated results using4indicators were similar. In1980s and12years of21st century, the influence on river runoffand sediment caused by human activities was more than precipitation change, the contributionrate were above70%. In1990s, the influence on runoff and sediment caused by humanactivities and precipitation change were almost the same, both occupied about50%ofreduction of river runoff and sediment Took1980s as reference period, the runoff reductioncaused by human activities was14.1×108m3/a, and the sediment reduction caused by humanactivities was2.5×108t/a. |
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